Various industrial operations require immersion of a product in hot liquids. In the electronics industry, for example, chemical baths are used for such purposes as etching and cleaning integrated circuit wafers. The liquid chemical must often be heated to a very high temperature and in many cases is highly corrosive. Thus certain components of the chemical bath must be formed of refractor materials which are also non-reactive to the liquid chemical.
A particularly advantageous form of chemical bath for such purposes is described in my copending U.S. patent application Ser. No. 07/434,709, filed Nov. 13, 1989 now U.S. Pat. No. 5,014,737 issued May 14, 1991 and entitled "Quartz Integrated Trough/Sump Recirculating Filtered High-Purity Chemical Bath, the specification and drawings of which are hereby incorporated by reference. A chemical bath of that form includes a liquid chemical receptacle with a first compartment which functions as a processing vessel for receiving the articles to be treated and a second compartment which forms a sump. A trough extends along the upper region of the receptacle to carry overflow from the processing vessel to the sump and a pump recirculates a filtered flow of the liquid from the sump back to the processing vessel. The receptacle, including the processing compartment, sump and trough, is preferably a unitized single component formed of a refractory material such as quartz. The lower region of the receptacle is situated within a casing or housing formed of a less brittle material that can be more easily fabricated into the desired shape, any of various plastics being suitable for the purpose.
The junction between the receptacle and the rim of the casing should be sealed to prevent entry of liquids, corrosive vapor or other fluids. In the prior construction this is provided for by situating the underside of the trough immediately above the rim of the casing and adhering a quantity of sealing mastic to the trough and casing rim.
Such a seal bonds three different materials together, the quartz or the like, the casing plastic and the mastic itself, each of which undergoes a different degree of thermal expansion in response to heating. This creates stresses that limit the life of the seal. Repeated thermal cycling tends to break the bond between the sealing mastic and the other materials and to disintegrate the mastic itself, thereby necessitating frequent replacement. The construction also limits the maximum liquid temperature in the chemical bath as extreme differential expansion of the seal components can break the relatively brittle quartz or the like.
A chemical bath construction in which the seal is more durable in the presence of high liquid temperatures and which tolerates higher liquid temperatures would be highly advantageous.
The present invention is directed to overcoming one or more of the problems discussed above.